Roman date to take in Caesar's second thoughts (5)
I believe the answer is:
ideas
'thoughts' is the definition.
(I know this)
'roman date to take in caesar's second' is the wordplay.
'roman date' becomes 'ides' (Roman calendar term, as in the Ides of March).
'to take in' is an insertion indicator.
'caesar's second' becomes 'a' (2nd letter of 'caesar').
'ides' enclosing 'a' is 'IDEAS'.
(Other definitions for ideas that I've seen before include "Thoughts, perceptions" , "Fancies" , "plans" , "Notions, concepts" , "thinking" .)